High up in the Italian Dolomite mountains, 90km north of Venice, the Vajont Dam was the scene of one of the 20th century’s worst engineering disasters. The tallest dam in the world when it was completed in 1959, at 262m, it was beset with problems from the beginning. On October 9, 1963, before it had even been completely filled, an enormous landslide (the 2km-long scar of which can still be clearly seen) sent 260 million cubic metres of mountainside into the lake behind the dam, causing a wave of water 250 metres high to spill over into the…